Friday, September 30, 2011

[Biology Form 5] Crossing Variants

What happens when plants with different variants are crossed?

For example, when we cross a tall plant with a short plant, will we get all tall offspring, a mixture or only short ones?

The factor determining the outcome is the genotypes of the parents.

The genotype is the combination of a pair of alleles (or genes) that an individual has for a particular characteristic.

The phenotype refers to the physical aspect manifested by the combination of a particular set of genes in the DNA.


Example:
Two pure breed garden pea plants - one tall and one short - are crossed. What are the possible phenotypes and genotypes of their offspring? tall is dominant over short. [T: tall allele and t: short allele]

Solution:

Thursday, September 29, 2011

[Biology Form 4] Gaseous Transfer

What happens to the composition of atmospheric air when it reaches the alveoli?

Some of the oxygen dissolves in the film of moisture covering the epithelium of the alveoli.

From here, it diffuses into the blood in a nearby capillary, and enters a red blood cell before combining with the haemoglobin therein.

The diagram below shows the blood vessels involved in the transport of gases in the lungs.


Information: Organ/structure and its description
  1. Bronchioles - The branched structures found at the end of each bronchus.

  2. Trachea - A tube supported by C-shaped rings of cartilage.

  3. Diaphragm - A dome-shaped sheet of muscle found at the bottom of the thorax.

  4. Alveoli - If spread out, these structures would cover the size of a tennis court.

  5. Ribs - The intercostal muscles are found between them.

  6. Epiglottis - This is a special flap that covers the tracheal opening when we eat and prevents food from entering the trachea.

  7. Bronchi - The two tubes found at the lower end of the trachea.

  8. Nose - Air enters our body through this organ.

  9. Pharynx - The passageway for air between the nose and the trachea.

  10. Blood capillaries - The structures found on the outside of the alveoli.

Nota Terkini